Fifa president Gianni Infantino yesterday said that breakaway Super League clubs cannot be "half in, half out" of the established football system, while Real Madrid supremo Florentino Perez insisted he is trying to "save football" with the move.
European football's governing body Uefa has threatened to ban the 12 clubs, who include Manchester United and Madrid, from domestic and international competition, with Infantino adding his voice to the backlash.
"We strongly disapprove ... if some go their own way then they must live with the consequences of their choice, either you are in, or you are out," Infantino told Uefa's Congress in Montreux, Switzerland.
"You cannot be half in and half out."
Uefa chief Aleksander Ceferin has not held back on his views of the renegade clubs, who will be guaranteed places in the new competition in contrast to the Champions League which requires teams to qualify via their domestic leagues.
Having labelled the competition a "spit in the face" of football fans, Ceferin insisted, however, that there is still time for reconciliation.
He said the owners of the English clubs made a "huge mistake."
"Some will say it is greed, others disdain, arrogance or complete ignorance of England's football culture but actually it doesn't matter.
"There is still time to change your mind. Everyone makes mistakes, English fans deserve to have you correct your mistake, they deserve respect."
There have been few voices that have backed the breakaway league, with owners of the 12 teams conspicuous by their absence.
The first senior figure of any club involved to publicly talk about the move was Perez - the new chairman of the Super League - who said football needed to evolve and adapt to the times.
"Whenever there is a change, there are always people who oppose it ... and we are doing this to save football at this critical moment," Perez said on Spanish television.
He added that clubs are hurt by the decrease in audiences, especially among the young, because of the "poor quality" of the matches.